Apparatus for measuring electrical resistances.



No. 858,335. PATENTED JUNE 25, 1907 S. EVERSHED. APPARATUS FOR MEASURING ELECTRICAL RESISTANGES.

APPLICATION FILED IEB.28, 1906.

4SHEI-1TSSHEET 1 W/7/1/Z355S ivvi/vrm? W flTTXS' PATENTED JUNE 1907f S. EVERSHBD. APPARATUS FOR MEASURING ELECTRICAL RESI STANGES.

APPLICATION FILED I'EB. 28, 1906.

4 SHEETSSHEET 2.

STANDARD OHMS W/ r/vfssfs No. 858,335. .PATENTED JUNE 25, 190?.

S. EVERSHED. APPARATUS FOR MEASURING ELECTRICAL RESISTANOES.

APPLICATION FILED H1328 1906.

4 SHEETS-SHEET 3.

" m/vE/v T No. 858,335. PATENTBD JUNE 25, 190? A s. EVERSHED. V APPARATUS FOR MEASURING ELECTRICAL RESISTANOES.

APPLICATION FILED FEB. 28, 1906.

4 SHEETS-SHEET 4.

STANDARD onms E E! @J If A l l N ITED STATES PATENT OFFICE. SYDNEYQEVERSHED, or CHISWICK, ENGLAND, ASSIGNOB "r HIMSELRAND EVERSHEDAND VIGNOLES' LIMITED, OF CHISWICK, ENGLAND, A con- PORATJIONoF GREAT BRITAIN AND iRELAND.

' ware/trusses msAsuRmer-1EovmoAL RESISTANQES.

No. ceases.

Specification 0! Letters Patent. E Application iileifl'ebrury 28,1906. Ber-id No. 503,556.

Patented June 25, 1907.

To all} whomfit may concern.- Bait known that I, SYDNEY Evnnsnsn, a sub ect of the 'of Great Britain and Ireland residing atC wicli, county of Middlesex, England, have invented new and useful Improvements in A aratus for Measurin 0 Electrical Resistanc s j of which the followis at specification.

his invention. relates to galvanometers, m ohmmeters and resistance boxes or rheostats and its objects are to facilitate the rapid measurement of resistances, by means of a coil controlled gelvanometer and any suitable ohm-reading rheostat, and to enable :5 tests for the location of faults in electric circuits to be carried out by means of a-high voltage with necess rily high resistances, whichwill reduce i tcrference from stray currents and electromotive forces to a mim. 2on'1um..-

My invention may be usefully applied to most of, the uslialresistance tests and is specially applicable to the resistance and fault-location tests required on telegraph 2 5 and telephone circuits.

To carry out my invention tests of conductor, resistance ma be made on the Wheatstone bridge prmciple'or by the differential galvanomcter method or other oknown principle, but in all cases, I use an improved form of g'alvanomcter made on the same principle as a two-coil ohmmeter; that -is to say with one coil performing the same function as the coil in an ordinary bridge 3 5 galvanometer or as the coils of a differential galvanometer, and with the other coil acting as the controlling force for the movable system. A current for the controlcoil is derived from the-same source as that employed I 40 for the currents inthe bridge or in the differential circuits as the cascmay be.

With my improved galvanomcter it is not ne'cessag to employ constant sources of current, an according to my invention 1 pro-' vide asuitable=hand dynamo for rovicling the necessary testing current. he dynamo is wound to give a much higher voltage -than is commonly em loyed to testing conductor resistance, an a high resistance is inserted in the armature circuit of the dynamo, so as to limit the current produced.

to a convenient and approximately constant value, no matter what value of resistance me be under test. .Thus, I obtain substan-. tial y the same sensibility for all tests through- 5 5 out a wide range of resistances. The irregular current due to unsteady rotation of the .hand dynamo, has no eilection the steadiness of the alvanometer deflection, since both the wor lring' coils and the control coil are aiiected to an equal degree.

Myim )YOVGCl galvanomcter and high-voltage hig -'resistance hand dynamo may be employed to greatadvantage in locating the position of faults on telegraph and other crrcuits by means of any of the well-known loop tests. 'l he diiiiculties often met with, in carrying out such-tests, owing to-earth currents and powerful currents straying from olcctric-tramwa' lines, are almosflentirely 7o eliminated by the very his esistance I am able to insert in m dynamo circuit. .For

example i may him my dynamo to give 200 volts, and a lab this voltage the resistance in the dynamo circuit may be asmuch as 10000 minus; with such avoltage and 'resistancc, stray currents are reduced toa nearly negligible value.

in order that my invention may be. the better .umlerstoml, 1 will nOwdescribe it with reference to the accompanying drawings, of which a Figure 1 shows my coil-controlled galvanomcter fitted inside a portable boxwith a hand dynamo and the necessa coils and 5 connections for Wheatstone bri ge test' Fig. 2 is a diagram of my coil controlled {1. vanometer arranged for working bg the ferential method and provided wit alternat-ive connections for insulation testirg. 9. 2 is a di am of my coil controll galvanometer si owing certain terminals dISOOH- nected and other two terminals connected.- Fig. 3 is a diagram of my coil controlled gal vanometcr and hand dynamo arr testing conductor resistances by the cat-- stone 'bridge method and fitted with a switch for converting the -galvanometerinto a direct reading ohrimleter for testing insu lation resistances. 9

In Fig 1; a is the working coil of a mo coil alvanometer and b is the control col whic is fixed upon the same axis asfq but withits magnetic axis at right angles It:

ed for Resistance coils c and d form the ratio arms of the Wheatstone bridge,and I show a; switch e for changing the ratio so as to-enable a wide range of resistances to be measured.

5 Current for testing is provided by a hand dynamo f operated by a winch handle 9 through the medium of suitable gearing. The dynamo may conveniently be wound to give a-high voltage and to reduce the current to a convenient 'value, I insert a highresistance h m the. armature circuit. When,the dynamo is wound to give as much as 200 volts l the resistance It may be as much as 10000 or 20000 ohms The control coil bis connected to the terminals of the dynamo, aresistance 'i bein inserted in its circuit adapted to re, duce t e current through the control coil to a suitable value.

Two pairs of terminals are provided; to

one pair 7' a suitableadjust-able resistance box 7c is to be connected, while the resistance, to be tested, 1 is connected to terminals m. The current is led in and out of theworking coil and the control coil by means-6f flexible conductorsw. I

The magnetic field for thev dynamo and the. moving coil galvanometer may be ,conveniently provided by a pair of permanent magnets n 0, but I do'notconfine myself to this arraement In ig. 2, I show the working coil of my galvanometer wound differentially in two parts a and a? as s own in Fig. 2, andsince these coils have, a most necessarily, a wind- 5 ing of copper wire, I provide a resistance 1) and p: in series with them, constructed of wire aving a negligible temperature-variation, so that the exact equality of the difi'erential coils may Le preserved independently 0 of temperature. In this diagram I show connections for locating a leak on the loop 1; the switch g enables one pole of the dynamo to be connected to an earth terminal 1' and so to earth, so that the usual method for ascer- 4 5 taining the position of the leak, namel by adding resistance to one end of the loop until the leak occupies the center of the circuit formed by the loo and the rheostat, may be carried out. I a. so show additional termi- 5o nals s and t which may be used for carrying out insulation testing as shown in Fig. 2";

' coil a then 'servin as a current coil of-an ohmmeter, and coi b as the pressure coil, it being understood of course that while the 5 5 insulation testing is being carried out the ter 'minals m, j and r are disconnected. A suitableresistance'u is inserted between the coiln and the terminal 8.

In Fig. 3, I show my coil controlled galva- 6o nometer adapted for working on the Wheat? stone bridge principle, and fitted with a 3- pole 2 way switch 0 which enables the workmg coil of the alvanometer to be discon-' nectcd from the ridge and connected to the -e al s. At the same time, the dynaml$ d fconnected irony the bridge and conncb'ted t -othe other terminal of, the working coil,;thus fcomgeriing the galvanomcter into a 2-coil ohrmnclefian d endblingthe insulation of any circuitcbrinedteil to the terminals .9 and t to be measured by direct reading on the scale of the gal'vano'meter.v When my c oil-' cor. LlOl led galvanometer is to be used in this way; I providc asuitable scale of ohms and megohms so that the reading of insulation resistance may be direct; theinfinity-point of the ohm scale is then used as the zcro or .fiducial mark of the galvanometer scale.

My apparatus may beemployedfor testi all ordinary resistances, and owing to my ga vano'meter' being'made dead beat there is no difi'iculty, in measuring circuits having moderate self induction or capacity but where it is'desired to measure the resistance of a rcuit having a very large time:constant, as for examplefthe field coil of ady namo, I use a. hand dynamo adapted "to provide aconstaiit electr' moti.ve "force and vperfectlysteady.current.

When tests are to be madefwith myinr proved apparatus, the operator 'turns thr an'dleof the dynamo with one hand,, an(.i while watching gthe deflectibn of the galvanometer he is able to adjust therheostatwith the other hand and eflectlan accurate balance with far greater rapidity than by any of the means heretofore available. 3 I claim and desire ,to secure by LettersPakentisz l T m 1. Apparatus for measuring i'esist an .-E" consisting of in combination, a=hand dynamn a Wheatstone bridge, a resistance box, a line of which theresistance'is to be'tested, and 'a coil controlled galyanometerjn which the control coil'is 'direc'tly connected between the two poles of aidynamo; the working coil bestone bridge a single ole of "the dynamo Wheatstone bridge and the Working 'coil of the galvanometer anda-thencepassing' to the other cle .of the dynamo; 4

2. combination, 'a hand dynamo, a Wheatstonebridge, and a: coil controlled galvanometer, in which the control coil is connamo, and the workin coil is connect (I to either end ofthe said eatstone'bridg 3. In apparatus for locating faults in combination, a high volta e dynamo of high resistance, a Wheatstone ridge-and a dead beatcoil controlled galvanometei', in which the control coil is connected to, the two poles of the said dynamo, and'the'worki coil of the galvanomete of the said Wheatstone bridge.

' Having now desc 'bed myinvention what bei divided between t e resistance box and i the line to be'measurcd, back to the 'nected between the two poles of the saidldy' r, is connected to eit er ending connected to opposite points of the Wheat- 4. In eombinationya hand (1 arm, and a v coil controlled galvanometer, tge control coil being connected between two poles of the dynamo, the working coil composed of two 5 differentially wound coils, the connection of these soils being distinct from the eonneo tions to the controlcoil, receiving-e charge from one pole divided between the resistance box and the line to be tested, while the rere turn is from the line between the two said assess 

